Concurrent Code Using Groovy

July 31, 2010

 
Summary

Presented are a few ways of coding a concurrent program using Java threading and also using a Communicating Sequential Processes (CSP) library.  They are written in the Groovy language. Used as an example is a simple lottery number generation application.

[intro],  [problem],  [Listings],  [simple thread],  [object lock],  
[executor],  [Fork/Join],  [jCSP],  [Actor],  [Declaritive CSP using Spring],  [Links],   [bottom of page]

Intro

In a prior blog post (Java Plain Old Concurrent Object) I wrote about a possible need for a higher level concurrency support in Java.   Here I give the program code that I used in September 2007 to learn more then the rudimentary Java concurrency concepts.

I managed to use CSP and the usual Java concurrent library support, and recently was about to try Actors using the new GPars library.  It was a good way to get a feel for each approach.  Note that it was not enough to become a concurrency expert; that was not a goal; still studying Goetz’s book Java Concurrency In Practice.

My first use of multitasking code was in C++ code I did in 1992:

… technical hurdles with the product, so I put it aside until I could get back to it. One thing that I was proud of was learning a little bit of Fuzzy Logic and using it as the controller. I even wrote a graphical simulator in the C++ language; threading was fun stuff. Watching the fuzzy sets behave like analog surfaces or neural EEG waves gave me the idea for the biomimicry aspects. — An Adaptive Controller Using Fuzzy Memory

Problem

For code example I used lottery number play generator.  Powerball is a U.S. multi-state lottery game.  A Powerball play is composed of 5 white balls in range 1 – 55 and one red ball in the range of 1 – 42.  As you can imagine the odds are extremely high that you could guess the Jackpot set (1 in 195,249,054).  The jackpot gets very large and that is a great enticement to forgo any sanity and “you can’t win if you don’t play” you know. 

If you enjoy the frills, ambiance, and clientele, gambling is a great way to throw away money.   For more on Lottery see: Lottery Links
back to top

Source Code

To simulate real random number generation, the program will continuously generate plays, but only produce the requested numbers of generated sets when the user clicks the enter key.  I’m assuming a user waiting a certain amount of time adds a random element to the PRNG being used.  Does it?  I don’t think so, but that’s another topic.

A few points:

  • The problem could have been solved without using concurrent approach.
  • The code could be optimized and made more Groovy.
  • I used the Eclipse IDE and the Groovy Eclipse Plugin.
  • Example code use at your own risk.  No correctness or quality guaranteed.

A Thread monitor view using VisualVM doesn’t show much, just six threads with four daemon ones.

We use the following batch file, which simply invokes the Main.groovy script.

@rem File: run.cmd
@rem Created 28 Dec 2008 J. Betancourt
call setEnv.cmd
groovy ..\src\main\groovy\net\cox\members\jbetancourt1\Main.groovy %*

The main script driver is shown in listing 1.  Two arguments are specified, how many dollars to lose and what type of concurrency approach to use.  Executing it with no arguments would give:

c:\Users\jbetancourt\Documents\projects\dev\ConcurrentGroovy-1\bin>run
usage: usage -t type -d dollars [-h]
 -d,--dollars    How many dollars to lose
 -h,--help       Usage information
 -t,--type       Type of threading

Options for '-t' are:
 "simple"    ----> "Using simple Threads"
 "lock"      ----> "Using lock"
 "executor"  ----> "Using Futures"
 "csp"       ----> "Using JCSP"
 "actor"     ----> "Using Actors"
Example: run -d 5 -t simple

And, here is a sample run:

c:\Users\jbetancourt\Documents\projects\dev\ConcurrentGroovy-1\bin>run -d 5 -t simple
Setting up games 5 using "simple"
The odds of winning jackpot are: 1 in 146,107,962.00
Enter return key

Number of games generated are: 5
 1:   7 11 14 23 34 PB:  9
 2:  21 22 27 28 55 PB: 21
 3:   2  9 30 37 46 PB: 30
 4:   7 49 50 51 53 PB: 30
 5:   9 18 24 40 42 PB: 32
Good luck!

Success?

Not really.   A funny thing about this code, if you invoke it and quickly hit the return key, it doesn’t work correctly.  Concurrent code can be hard to craft.
Example:

>run -d 5 -t executor
Setting up games 5 using "executor"
Press the Enter key on keyboard

Number of games generated are: 1
 1:  18 20 22 27 41 PB: 25
Good luck!

Listing 1 Main driver class:

package net.cox.members.jbetancourt1;

import org.apache.commons.collections.buffer.CircularFifoBuffer
import org.apache.commons.collections.Buffer
import java.security.SecureRandom
import org.apache.commons.collections.BufferUtils

/**
 * Generate Powerball plays.
 * Required libraries:
 * - Commons CLI
 * - Commons collection
 *
 * A Powerball play is composed of 5 white balls in range 1 - 55
 * and one red ball in the range of 1 - 42
 * This script gets how many games to play, then
 * continually generates this number of games
 * and adds them into a circular buffer.  This is
 * repeated until the user hits a key, which
 * interrupts the generation thread and dumps the results.
 *
 * A circular buffer is used since the results are
 * only needed when the user hits a key,
 * thereby making it "random".  In actuality,
 * since we are using a psuedo-random
 * generator, this is still not true random.
 * There is no way to improve the odds of
 * picking the correct numbers for a lottery game.
 */
 class Main{
 def apps = [
    "simple": [new GuessSimple(),"Using simple Threads"],
    "lock":   [new GuessWithLock(),"Using lock"],
    "executor": [new GuessWithExecutor(),"Using Futures"],
    "csp": [new GuessCSP(),"Using JCSP"],
    "actor" : [new GuessActor(),"Using Actors"]
 ]

 /** Main entry point */
 static main(args){
    def main = new Main()

    def options = main.parseArguments(args)
    if((options != null ) && options.d && options.t){
        println "Setting up game" + (options.d>0? "s": "") +
        " ${options.d} using \"${options.t}\""
        def dollars = Integer.parseInt(options.d)
        def games = BufferUtils.synchronizedBuffer(
           new CircularFifoBuffer(dollars))

           def threadType = ""
           if(options.t){
               threadType = options.t
           }

           def guess = main.apps[threadType][0]
                guess.generate(dollars,games)
    }

    System.exit(0)
 } // end main

 /****************************************************************************
 * Using CLI builder, parse the command line.
 */
 def OptionAccessor parseArguments(String[] args){
    def cli = new CliBuilder(usage: 'usage -t type -d dollars [-h]')
    cli.h(longOpt: 'help', 'Usage information')
    cli.t(longOpt: 'type', 'Type of threading',args:1)
    cli.d(longOpt: 'dollars','How many dollars to lose',args:1,required:false)
    def options = cli.parse(args)

    if(options == null || options.getOptions().size() == 0 || options.h){
         cli.usage()
         println "\nOptions for '-t' are: "
                    apps.each{
         println("\t\"${it.key}\"".
              padRight(12) + " ----> \"${it.value[1]}\"")
    }
    println "\nExample: run -d 5 -t simple"
    return options
  }

  return options
 }
} // end class Main

Listing 2 Base class:

<pre>package net.cox.members.jbetancourt1;

import org.apache.commons.collections.buffer.CircularFifoBuffer
import org.apache.commons.collections.Buffer
import java.security.SecureRandom
import org.apache.commons.collections.BufferUtils

/**
 *
 */
class GuessBase{
 def whiteBalls = [0]
 def redBalls = [0]
 def random = new SecureRandom()
 //each element is an array of 0-4 white ball values and 5 is the red ball value.
 def games //= BufferUtils.synchronizedBuffer(new CircularFifoBuffer(dollars))

 def createBallSets(){
      def i = 0
      for(j in 1..55){
        whiteBalls[i++] = j
      }
      i = 0
      for(j in 1..42){
         redBalls[i++] = j
      }
 }

 /** Pick the set of white balls */
 def pickWhite(){
     def array = []
     array.addAll(whiteBalls)
     Collections.shuffle(array,random)
     return array[0..4]
 }

 /** swap two elements in a list */
 def swapElements(list,i,j){
      def temp = list[i]
      list[i] = list[j]
      list[j] = temp
 }

 /**  Pick the single red 'powerball'. */
 def pickRed(){
      int offset = random.nextInt(redBalls.size())
      return redBalls[offset]
 }

 def showGames(){
     def gamesSorted = games.sort(){a,b -> a[5] <=> b[5]}
     def rownum = 1
     println "Number of games generated are: ${games.size()}"
     for (loop in gamesSorted){
       print ((rownum++ + ": ").padLeft(8))
       for(x in (  loop[0..4]).sort()  ){
         print ((x.toString()).padLeft(3))
       }
       println " PB:" + ((loop[5]).toString()).padLeft(3)
     }
     println "Good luck!"
 }

} // end class GuessBase

Listing 3 Using simple Java Thread class:

package net.cox.members.jbetancourt1;

/**
 * Example that uses a simple 'inline' thread.
 */
class GuessSimple extends GuessBase{

 /** create d guesses and store into games array */
 def synchronized generate(d,games){
   this.games = games
   createBallSets()

   def worker = new Thread();
   worker.setDaemon(true);

   worker.start{ // Groovy allows closure here.
     while(!Thread.currentThread().isInterrupted()){
       def w = pickWhite()
       def r = pickRed()
       games.add((Object)(w+r))
       random.setSeed(System.currentTimeMillis());
     }
   }

  println "The odds of winning jackpot are: 1 in 146,107,962.00\nEnter return key"
  new InputStreamReader(System.in).readLine()

  worker.interrupt()
  Thread.sleep(1000) // required!
  showGames()
 }
} // End of GuessSimple.groovy

Listing 4 Using Object lock:


package net.cox.members.jbetancourt1;

/**
 *
 */
class GuessWithLock extends GuessBase{
  def lock = new Object() // for thread synchronization
  /** create d guesses and store into games array */
  def generate(d,games){
  this.games = games
  createBallSets()

  def worker = new Thread(){
     void run(){
       while(!Thread.currentThread().isInterrupted()){
         def w = pickWhite()
         def r = pickRed()
         games.add((Object)(w+r))
         random.setSeed(System.currentTimeMillis());
       }
       synchronized(lock){
          lock.notify()
       }
     }
 }

 worker.start()

 println "The odds of winning jackpot are: 1 in 146,107,962.00"
 println "Enter any key<cr>"
 new InputStreamReader(System.in).readLine()
 worker.interrupt()
 showGames()
 }
}

Listing 5 Using Executor:

/**
* File: GuessWithExecutor.groovy
* Author: Josef Betancourt
* Date:  9/1/2007
*
*/
package net.cox.members.jbetancourt1;

import org.apache.commons.collections.*
import java.util.concurrent.*

/**
 * Generate powerball plays using Executor.
 */
 class GuessWithExecutor extends GuessBase {

 /** create d guesses and store into games array */
 def generate(d,games){
       def dollars = d
       try{
         def exec = Executors.newSingleThreadExecutor()
         def gen = new GameGenerator<Buffer>(dollars,games)
         gen.createBallSets()
         def future = exec.submit(gen)
         println "Press the Enter key on keyboard"
         new InputStreamReader(System.in).readLine()
         exec.shutdownNow()
         waitForTermination(exec,100,10) // 100ms, max of 10 tries

         try{
           def buffer = future.get()
           def exec2 = Executors.newSingleThreadExecutor()
           exec2.execute(new GenerateReport(buffer))
           exec2.shutdown()
         }catch(ExecutionException ignore){
            ignore.printStackTrace()
         }
       }catch(Exception ex){
           ex.printStackTrace()
       }
 }

 /**
 *
 * @param exec the Executor
 * @param time how long to wait
 * @param unit unit of time
 * @param tries how many times to wait
 */
 def waitForTermination(exec,time,tries) throws Exception {
    def count = 0
    while(!exec.awaitTermination(time, TimeUnit.MILLISECONDS)){
        if(count++ >= tries){
           break
        }
    }
 }

 } // end class GuessWithExecutor

 /**
 * A Callable that generates games until interrupted.
 */
 def class GameGenerator extends GuessBase implements Callable {
       def GameGenerator(dollars,games){
                this.games = games
       }

      /**
       * Create d guesses and store into games array.
       * @see java.util.concurrent.Callable#call()
       */
     public Object call() throws Exception {
         while(!Thread.currentThread().isInterrupted()){
             def w = pickWhite()
            def r = pickRed()
            games.add((Object)(w+r))
            random.setSeed(System.currentTimeMillis());
         }
         return games
 }

 }  // end class GameGenerator

 /**
 * Class to render the results
 */
 def class GenerateReport extends GuessBase implements Runnable {
      def GenerateReport(Buffer games){
              this.games = games
      }

      public void run(){
         showGames()
     }
} // end class GenerateReport

Listing 6 Using Fork/Join:


// to do:  approach will be to fork each required game set into its own thread, then join them to get the final result.  Crazy, but a way to learn about Fork/Join and have sample code.

CSP

Some experts are touting the benefits of CSP. Below I use the jCSP library to create a network of processes that collaborate to solve the same problem. Note that some of the people involved in jCSP are adding some CSP support to GPar.

Listing 7 Using jCSP:

/**
* File: CspGuess.groovy
* Author: Josef Betancourt
* Date:  9/1/2007
*
*
*/

package net.cox.members.jbetancourt1;

import jcsp.lang.*;

/**
 * Generate powerball plays using CSP.
 *
 * This version of the example uses the JCSP library.  Note
 * that unlike the other examples, there is an explicit
 * declaration of a 'network'.
 *
 * Required libraries:
 * - JCSP ver. 1.0-rc8 CSP library in Java:
 * <a href="http://www.cs.ukc.ac.uk/projects/ofa/jcsp"></a><br/>
 *
 * Uses PAR and ALT methods presented in:
 * <a href="http://www.soc.napier.ac.uk/publication/op/getpublication/publicationid/9097759">
 * "Groovy Parallel!  A Return to the Spirit of occam?"</a>
 * by Jon KERRIDGE, Ken BARCLAY, and John SAVAGE
 * The School of Computing, Napier University, Edinburgh EH10 5DT in
 * Communicating Process Architectures 2005 13
 * Jan Broenink, Herman Roebbers, Johan Sunter, Peter Welch, and David Wood (Eds.)
 * IOS Press, 2005
 *
 * Perhaps, a better approach is possible using actors?  See for example,
 * <a href="http://gpars.codehaus.org/">Groovy Parallel Systems</a>
 *
 */
class GuessCSP extends GuessBase {
 def generate(dollars,games){
       def suspendChannel = new One2OneChannel()
       def resultChannel = new One2OneChannel()

       // Create the CSP network and run it.
       new PAR(  [
            new GameProcess(suspendChannel,resultChannel,games,dollars),
            new UserInputProcess(suspendChannel),
            new ReportProcess(resultChannel)]
       ).run()
 }

}

/** process that generates games */
def class GameProcess extends GuessBase implements CSProcess{
    def out
    def suspend
    def dollars

    /**  Create the process instance */
    def GameProcess(done,out,games,dollars){
       this.dollars = dollars
       this.suspend = done
       this.out = out
       this.games = games
       createBallSets()
    }

    /** run the process network */
    public void run(){
       def alternative = new ALT([suspend, new Skipper()])
       def STOPPING=0, RUNNING=1
       println "Creating  ${dollars} game${(dollars>0? "s": "")}  "
       def suspended = false
       while (!suspended){
          switch (alternative.priSelect ())
             {
               case STOPPING:
                 suspend.read();
                 if(games.size()>0){
                      suspended = true;
                      out.write(games)
                 }
                 break;
               case RUNNING:
                 def w = pickWhite()
                 def r = pickRed()
                 games.add((Object)(w+r))
                 random.setSeed(System.currentTimeMillis());
                 break
             }
      }
 } // end run()

} // end GameProcess process

/** Process that gets the user input */
def class UserInputProcess implements CSProcess{
     def suspend

     def UserInputProcess(done){
            this.suspend = done
     }

     public void run(){
              println "Enter any key<cr>"
              new InputStreamReader(System.in).readLine()
              suspend.write(new Object())
     }
} // end UserInputProcess process

/**
 * Process to render the results to console
 */
def class ReportProcess extends GuessBase implements CSProcess{
 def input

 def ReportProcess(input){
     this.input = input
 }

 public void run(){
     games = input.read() // get result via channel only
     showGames()
 }
} // end of ReportProcess process

/**
 * PAR A Groovyish Parallel.
 */
def private class PAR extends Parallel {
       PAR(processList){
            super( processList.toArray(new CSProcess[0]))
       }
}

/**
 * ALT A Groovyish Alternative.
 */
def private class ALT extends Alternative {
       ALT (guardList) {
              super( guardList.toArray(new Guard[0]) )
       }
}
// end of CspGuess.groovy

Actor

I started to look into the Actor approach. Below is the start of code to solve the same problem. Even with the few lines of code, attempts to run it give an an exception, and classpath and other easy fixes do not solve it. On my todo list.

Setting up games 5 using "actor"
start
Caught: groovy.lang.MissingMethodException: No signature of method: static groovyx.gpars.actor.Actor.actor() is applicable for argument types: (net.cox.members.jbetancourt1.GuessActor$_generate_closure1) values: [net.cox.members.jbetancourt1.GuessActor$_generate_closure1@1fe571f]
Possible solutions: stop(), wait(), start(), any(), call(java.lang.Object), wait(long)
	at net.cox.members.jbetancourt1.GuessActor.generate(GuessActor.groovy:55)
	at net.cox.members.jbetancourt1.Main.main(Main.groovy:63)

Listing 8 Using Actors:

package net.cox.members.jbetancourt1
//import static groovyx.gpars.actor.Actors.actor
import groovyx.gpars.actor.*
import groovyx.gpars.actor.Actor.*
// @Grab(group='org.codehaus.gpars', module='gpars', version='0.9')
// @GrabResolver(name='jboss', root='http://repository.jboss.org/maven2/')

/**
 */
class GuessActor extends GuessBase  {
	def main = new GuessActor()
	        def dollars
	        def games
	        main.generate(dollars, games)
        }

	def generate(dollars,games){
		println "start"

		def gen = Actor.actor { index ->
			loop {
				react {message ->
					if (message instanceof String) reply "got it"
					else stop()
				}
			}
		}

} // end of class GuessActor


Declarative CSP Using Spring

While experimenting I had an idea that ordinary Java beans could be used in a CSP network with suitable object wrappers or weaving.  That is, an ordinary POJO could be wrapped to appear as a Process, just hook up the bean’s entry point for service into the CSP channel end points.  This would be similar to the way that ordinary beans can be annotated to behave as Active Objects in the GPars Groovy library.

Below is the Spring Framework configuration file that does this for this software example.  The code for the wrapper objects are not included here, too kludgey.

Off topic: The XML language config of Spring is looking long in tooth. Good thing Spring now supports annotations and Java config. Time for a Groovy builder approach too?.

Update:

Listing 9 bean configuration file:

<?xml version="1.0" encoding="UTF-8"?>
<!--
 File: applicationContext.xml
 Spring Framework based bean definitions for JCSP example program.
 Author: Josef Betancourt
 Date:  9/19/2007
-->
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xmlns:lang="http://www.springframework.org/schema/lang"  xmlns:util="http://www.springframework.org/schema/util"
 xsi:schemaLocation="http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans-2.0.xsd


http://www.springframework.org/schema/lang


http://www.springframework.org/schema/lang/spring-lang-2.0.xsd


http://www.springframework.org/schema/util


http://www.springframework.org/schema/util/spring-util-2.0.xsd">

 <!-- ========================================================= -->
 <!-- CSP NETWORK -->
 <!-- ========================================================= -->
 <bean name="network" dependency-check="objects" class="jcsp.lang.Parallel">
     <constructor-arg>
         <list>
              <ref bean="gameProcess" />
              <ref bean="reportProcess" />
              <ref bean="userInputProcess" />
              <ref bean="progressProcess"/>
         </list>
     </constructor-arg>
 </bean>

 <!-- ========================================================= -->
 <!-- CHANNELS -->
 <!-- ========================================================= -->
 <bean name="suspendChannel" class="jcsp.lang.One2OneChannel"/>
 <bean name="outputChannel" class="jcsp.lang.One2OneChannel"/>
 <bean name="progressChannel" class="jcsp.lang.One2OneChannel"/>
 <bean name="skipperChannel" class="jcsp.lang.Skip"/>

 <!-- ========================================================= -->
 <!-- GUARDS  -->
 <!-- ========================================================= -->
 <bean name="alternative" class="jcsp.lang.Alternative" dependency-check="objects">
        <constructor-arg>
            <list>
               <ref bean="suspendChannel" />
               <ref bean="skipperChannel" />
            </list>
        </constructor-arg>
 </bean>

 <!-- ========================================================= -->
 <!-- POJOs -->
 <!-- ========================================================= -->
 <!--  Creates the game generator, but it is setup programmatically
 since it needs the user supplied number of games to play, see GameGenerator.setup(int).
 -->
 <bean name="gameGenerator" class="net.cox.members.jbetancourt.pb.game.GameGenerator">
      <property name="random">
         <bean class="java.security.SecureRandom"/></property>
         <property name="maxRed" value="42" />
         <property name="maxWhite" value="55" />
 </bean>

 <!-- ========================================================= -->
 <!-- PROCESSES -->
 <!-- ========================================================= -->
 <!-- Receives signal from user to accept current generated game sets.
 -->
 <bean name="userInputProcess" init-method="init" class="net.cox.members.jbetancourt.pb.process.JCspSingleShotProxy">
    <property name="outputChannel" ref="suspendChannel" />
    <property name="methodName" value="run"/>
    <property name="target">
            <bean class="net.cox.members.jbetancourt.pb.game.KeyListener" scope="prototype"/>
    </property>
 </bean>

 <!--  Game generator.  Communicates with input and report processes.
 -->
 <bean name="gameProcess" dependency-check="objects"
            class="net.cox.members.jbetancourt1.pb.process.GameProcess">
     <property name="alternative" ref="alternative" />
     <property name="suspendChannelIn" ref="suspendChannel" />
     <property name="reportChannelOut" ref="outputChannel" />
     <property name="progressChannelOut" ref="progressChannel"/>
     <property name="gameGenerator" ref="gameGenerator"/>
     <property name="showInterim" value="false"></property>
 </bean>

 <!-- Output results to console.
 -->
 <bean name="reportProcess" dependency-check="objects"
         class="net.cox.members.jbetancourt1.pb.process.ReportProcess" scope="prototype">
       <property name="input" ref="outputChannel" />
 </bean>

 <!-- Output interim results to console
 -->
 <bean name="progressProcess" dependency-check="objects"
    class="net.cox.members.jbetancourt1.pb.process.ReportProcess" scope="prototype">
      <property name="input" ref="progressChannel" />
 </bean>

</beans>

Listing 10 Java main to load the network:

package net.cox.members.jbetancourt1.pb;

import jcsp.lang.Parallel;
import net.cox.members.jbetancourt1.pb.game.GameGenerator;

import org.apache.commons.cli.*;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

/**
 * 
 * Main program.
 * 
 * @author JBetancourt
 * 
 */
public class Main {
    private static final String TITLE = 
    "====== Lottery Generator using JCSP and Spring ============";
    private static Parallel network;
    private static ApplicationContext context;

    /**
     * Entry point for running the Guess application. Parses 
     * command line for number of games to play, loads 
     * wired application using Spring Framework
     * based IoC, sets up game array, and then starts 
     * the network of processes. 
     * @param args
     */
    public static void main(String[] args) {
        System.out.println(TITLE);
        int dollars = parseCommandLine(args);
        if ( dollars == 0 ) {
            return;
        }

        context = new ClassPathXmlApplicationContext(
            new String[] { "applicationContext.xml"});
        
        GameGenerator gen = (GameGenerator) context.
        getBean("gameGenerator");
        gen.setup(dollars);

        network = (Parallel) context.getBean("network");
        network.run();
    }

    /**
     */
    private static int parseCommandLine(String[] args) {
        ... ellided ...
    }

}

Further Reading

Lottery Links


Java Plain Old Concurrent Object

July 29, 2010

Abstract

This blog post reiterates the existing critique of the concurrency support in the Java platform and language: that the low level thread and shared memory features should be improved upon with one or more high-level concurrency frameworks. Some of the competing frameworks are listed, and further references are given.

CR Categories: D1.3 [Concurrent Programming]; D.1.5 [Object-oriented Programming]; D.2.2 [Design Tools and Techniques]: Design Tools and Techniques — Software libraries;D3.2 [Language Classifications]: Concurrent, distributed, and parallel languages;D.3.3 [Language Constructs and Features]: Concurrent programming structures;

Keywords and Phrases: concurrency, Java, Actor Model, threads, Component based software engineering, Concurrent object-oriented programming, Distributed systems, Java CSP, CCS, multiprocessor

This is an excerpt from a document I wrote about three years ago.  The doc was in a Java Specification Request (JSR) format and from time to time I updated the link section as I came upon interesting references.   Maybe someone will find it interesting or it will spark a new idea for a project. In a later post I give some examples of concurrent code using the Groovy language.

Intro

The Java Platform has built-in support for concurrent programming. At the time of Java’s birth this was very big deal. But, is it now time to build upon this by the creation of a requirements document for high-level concurrency support in the Java language? Could this bring Java closer to a Concurrent Object-Oriented Language (COOL)?

Well, since I’m not a concurrency subject matter expert, just a working stiff developer, I will leave that to others, and just put my two cents here. What prompted me even looking into this subject was my experience on a few projects that required concurrency support.

What is needed is a survey or summary of what exactly are the issues, what is available, what their application areas are, and what are the development options. Some of initial tasks I see, in no particular order, are:

  • State the problem and application scope.
  • Provide use-cases.
  • Create project
    • wiki, forums, etc.
    • conference
  • Limit the scope of the effort.
  • Identify solution categories.
  • Identify solution selection criteria.
  • Testing and management requirements.
  • Measures, such as Performance and scalability.
  • Tools.

One possible conclusion is that there is no need for a ‘higher’ level concurrency support in Java or that this should evolve on its own before attempts at standardization are attempted.

Problem

One thing has been left out of the OO frenzy is the concept of a process. There are two manifestations of this: Methodology and Concurrency. In the methodological realm, ‘process’, which was part of data-flow analysis, is practically missing from modern analysis (as typified by OOP/UML derived methods). And even now, modular approaches, are still divorced from concurrency concerns. For example, OSGi fortunately brings back modularity to the Java environment. As stated by Kriens:

“Why is modular important? Well, if there is one consistent lesson in all our technology trends over the past 50 years then it is high cohesion and low coupling. Structured programming advocated this; OO forgot it for some time ….” — Peter Kriens, http://forum.springframework.org/showpost.php?p=138459&postcount=2

Yet, even in OSGi, a module is still at the mercy of unconstrained concurrency effects:

“OSGi … does not provide a thread of execution to each bundle. Events are delivered to bundles through certain interfaces, but no guarantees are made about which thread event delivery occurs on. Generally, event callbacks are required to finish quickly and should not make calls back into the OSGi framework to avoid possible deadlock. It is common, therefore, for bundles to start one or more threads in order to get work done.” — Oliver Goldman, “Multithreading, Java, & OSGi”

Welch calls this “unconstrained OO”:

“In unconstrained OO, threads and objects are orthogonal notions — sometimes dangerously competitive. Threads have no internal structure and can cross object boundaries in spaghetti-like trails that relate objects together in a way that has little correspondence to the original OO design. ” – Peter H. Welch in Javadocs for jcsp.lang.CSProcess of the JCSP library

And, others give similar critiques:

All object methods have to be invoked directly (or indirectly) by an external thread of control – they have to be caller-oriented (a somewhat curious property of so-called object oriented systems). — P.H Welsh (“Process Oriented Design for Java: Concurrency for All”)

“In standard OO, if you hold a reference to friend, and you wish to invoke the borrowMoney() method, then the call friend.borrowMoney() is executed in your own thread of control, not in a separate thread (or in friend’s thread), thus breaking all similarity to the way the real world works.” — (Oprean and Pederson, 2008).

“Although the development of parallel languages began around 1972, it did not stop here. Today we have three major communication paradigms: monitors, remote procedures, and message passing. Any one of them would have been a vast improvement over Java’s insecure variant of shared classes. As it is, Java ignores the last twenty-five years of research in parallel languages.”
– JAVA’S INSECURE PARALLELISM by Per Brinch Hansen (1999)

“However, I think Java needs to change. When it was first released, its number one competitor was C++, and Java walked all over it in terms of support for concurrency. Threads in the standard library! Syntactic support for critical blocks! Implicit locks in every object! Now, Java’s number one competitor is C#, which is increasingly starting to look like a functional language. Also languages like Erlang and Haskell have concurrency primitives that walk all over Java’s (I particularly love Haskell’s composable memory transactions). I hope this is something that is addressed in Java 7, but I fear it won’t be…” — Neil Bartlett

A higher level concurrency support in Java will allow a more approachable use of concurrent development. Though the concurrency implementation in Java is a vast improvment over what was available in a popular language at the time, we are now seeing more interests in other approaches as shown in Scala, Erlang, Kilim, Akka, GPars, Haskell, and others.

A standard would then allow, within reason, the sharing of development expertise and common patterns and idioms among the different languages and frameworks. For example, could an Actor in Scala be behaviorially the same as an Actor in plain old Java?

We are also seeing multiple processor cores being used to continue the improvment in thruput since thermal and process limititions have reduced growth. These will also allow true parallism. A high-end actual product, Sparc T3, the Sun Microelectronics version of the chip multi-threaded (CMT) processor, will be capable of forming a quad core SOC (System on Chip) that offers 512 hardware threads. Even on personal desktop systems, we already have quad cores and soon hexacores will be commonplace in the high end, such as the Intel Nehalem-EX. (Note that concurrency and parallelism are not the same thing).

Update: This was written a while back. In the interim, Oracle bought Sun and in the process canceled the Rock high-end CMT based processor design. Yet, Oracle said they will continue to support the upcoming SPARC CMT versions. Interesting discussion is found here. Intel and AMD have not stood still. AMD, for example, is promising a 16 core “Interlagos” chip soon. On the mobile side, ARM and others are also producing multicore systems.

Plain Old Concurrent Component

Instead of just reusing existing terms, I can call this new concurrency support a Concurrent Component. A component is more similar to an OS process, whereas internally it may incorporate light weight threads.

A possible conceptual view of a Component or Plain Old Concurrent Object (POCO) is shown in figure 1 below . Note that this is intentionally reminiscent of a Programmable Logic Device (PLD) block diagram. Each block is an optional ‘concern’ that crosscuts each object that is part of the component. The nested objects can share state and optionally will execute within a fine-grain concurrency kernel. The external control communication is via interfaces that expose the Component API, whereas the actual messaging embeds the application API that the component instantiation provides. This is somewhat of the flavor of Cox’s Software IC concept (ref?). This is also similar to various old Microsoft COM models. In future, it’s even conceivable that each POCO could have its own core assigned in an dynamically created application specific multicore processor implemented in nanoprocessor FPGA.

And, yes the diagram is just my brain’s core dump on the subject. Would require more work to explore this further, and determine what would really make sense.

POCO

Concurrent Component

Why isn’t this need met by existing specifications?

Currently, developers can use the concurrency control constructs that are provided in the Java language itself. Many experts consider these too low level for some applications and for use by the average developer (in terms of development effort, correctness, and failure potentials):

Use Erlang-Style Concurrency. The Java concurrency primitives like locks and synchronized have been proven to be too low level and often to hard to use. There are better ways to write concurrent code. Erlang Style concurrency is one of them – in Java there are many ways to achive this in Java – I’ve written about them here. Newer ones are Akka and Actorom. You can also use Join/Fork or the myriad of data structures in java.util.concurrent. —- Stephan Schmidt in Go Ahead: Next Generation Java Programming Style

In Java 5 and above one uses the new java.util.concurrent utilities. These offer a powerful and relatively accessible API such as the Executor and the Fork/Join frameworks. However, though the latter were a significant improvement, their use still require advanced skills and really only offer the means to create application specific or JVM language based concurrency frameworks.

Even with concurrency updates in Java 6 and Java 7, the Java language doesn’t make parallel programming particularly easy. Java threads, synchronized blocks, wait/ notify, and the java.util.concurrent package all have their place, but Java developers pressed to meet the capacity of multi-core systems are turning to techniques pioneered in other languages.

— “A Java actor library for parallel execution

Some languages or libraries, such as Scala (?) and JCSP even use the underlying concurrency support in Java to create the respective ‘active’ object concurrency extensions. See for instance this presentation by Doug Lea, “Engineering Fine-Grained Parallelism Support for Java 7″.

Note that introducing a higher level of abstraction will not necessarily reduce the need for skilled engineering. In fact, it may increase that need until the patterns, methodologies, measurement, and tool sets catch up and support the new framework. Of course, many other concerns are important, such as performance.

Underlying technology or technologies:

There is a rich history in both industrial and academic research into the theory and practices of concurrency. In the fifty plus years of this, surely there must be more that can be used in Java then Monitors, semaphores and other low level tools.

Some examples are Communicating Sequential Processes (CSP), Calculus of communicating systems (CCS), and all the ‘proven’ concurrent support already found in other languages, among them, Occam, Go, Erlang, Haskell, Esterel, Scala, and many others in the academic research community. There is even one observation that the current Monitor implementation in Java itself could more fully embrace the original theoretical Monitor concept.

Of course, as in anything else, there is hype and fashion in software too. Thus, some approaches are touted as fixing deadlocks and other problems, when they don’t.

Related Projects:

· Disruptor – Concurrent Programming Framework
· LMAX: “The LMAX Architecture“, Fowler, M., http://martinfowler.com/articles/lmax.html
· CQRS: CQRS, Fowler, M., http://martinfowler.com/bliki/CQRS.html
· Akka: http://akkasource.org/
· Multiverse: http://multiverse.codehaus.org/overview.html
· REAL TIME OPERATING SYSTEM BASED ON ACTIVE OBJECT
· ESTEREL: http://www-sop.inria.fr/meije/esterel/esterel-eng.html
· Staged event-driven architecture (SEDA)
· CSP: http://www.usingcsp.com/cspbook.pdf
· Kilim: http://www.malhar.net/sriram/kilim/index.html
· JCSP: http://www.cs.ukc.ac.uk/projects/ofa/jcsp
· JVSTM: http://web.ist.utl.pt/joao.cachopo/jvstm/
· Clojure: http://clojure.org/concurrent_programming
· “Gpars: http://gpars.codehaus.org/
· Groovy Parallel: http://www.dcs.napier.ac.uk/~cs10/GroovyParallel/
· Scala: http://www.scala-lang.org/
· Triveni: http://webpages.cs.luc.edu/~laufer/triveni/
· ActorFoundry project, http://osl.cs.uiuc.edu/af/
· “Jetlang, Message based concurrency for Java” http://code.google.com/p/jetlang/
· Jsasb, adds event-driven programming paradigm to Java, https://jsasb.dev.java.net/
· Node.js: http://nodejs.org/
. Er.js: Er.js: Erlang-in-JavaScript
· MPJ: Java for High Performance Computing, http://mpj-express.org/
· FunctionalJava, accessed on 3/2/2009 at http://functionaljava.org/
· JAVACT : a Java middleware for mobile adaptive agents, accessed on 3/2/2009 on 3/2/2009 at http://www.irit.fr/PERSONNEL/SMAC/arcangeli/JavAct.html
· Threading in COM, accessed on 3/2/2009 at http://en.wikipedia.org/wiki/Component_Object_Model#Threading_in_COM
· http://www.transterpreter.org/
· http://supertech.csail.mit.edu/cilk/
· TBB: http://www.threadingbuildingblocks.org/
· JConch: http://code.google.com/p/jconch/
· JAC: http://www.inf.fu-berlin.de/inst/ag-ss/jac/
· X10: http://docs.codehaus.org/display/XTENLANG
· COSA: http://www.rebelscience.org/Cosas/COSA.htm
· BAM: http://caucho.com/resin/doc/bam.xtp
· Concurrent Programming Research Group, http://mypages.iit.edu/~concur/
· JCarder, http://www.jcarder.org/
· Go, http://golang.org/doc/go_lang_faq.html#concurrency
· Panini: http://www.cs.iastate.edu/~design/projects/panini/
·

Further Reading

Below are a few easily obtainable links found on-line. (To do: use standard style guide like IEEE Standard and Chicago).

· Coarse-grained locks and Transactional Synchronization explained

· Concepts compared

· “Joe Duffy on the Future of Concurrency and Parallelism

· Dr. Dobb’s Report: Real-Time Ready Java

· Actors Make Better Observers

· Talking about Akka, Scala and life with Jonas Bonér

· Miller, Alex; Comparing concurrent frameworks

· Lea, Doug; “Engineering Fine-Grained Parallelism Support for Java 7″, http://www.dzone.com/links/r/engineering_finegrained_parallelism_in_java.html

· Milewsk, Bartosz; “Beyond Locks and Messages: The Future of Concurrent Programming”, http://bartoszmilewski.wordpress.com/2010/08/02/beyond-locks-and-messages-the-future-of-concurrent-programming/

· Wiger, Ulf; “Death by Accidental Complexity”, http://lambda-the-ultimate.org/node/1630

· “Erlang concurrency: why asynchronious messages?”, http://lambda-the-ultimate.org/node/1630″>http://lambda-the-ultimate.org/node/1630

· Merritt, Eric;”A Brief Overview of Concurrency.”, http://erlware.blogspot.com/2010/07/brief-overview-of-concurrency.html

· Kuppusamy, Rmsundar; “Is concurrency such a complex thing in real world applications?”, http://www.dzone.com/links/r/is_concurrency_such_a_complex_thing_in_real_world.html; Comments on the article are very informative.

· Kabutz, Heinz; “Deadlocks through Cyclic Dependencies”, http://www.javaspecialists.eu/archive/Issue184.html

· Jackson, Joab, “Microsoft Windows architect says ditch the kernel”, http://news.techworld.com/operating-systems/3217766/microsoft-windows-architect-says-ditch-the-kernel/?olo=rss

· Breshears, Clay, “Across the wide Concurrency”, http://software.intel.com/en-us/blogs/2010/05/17/across-the-wide-concurrency/

· Dibyendu Roy, “Rethinking Multi-Threaded Design Principles”, [Weblog entry.] Java.net. 3 Mar 2010. (http://today.java.net/article/2010/03/03/rethinking-multi-threaded-design-priniciples). 5 Mar 2010.

· Mordani, Rajiv; “Asynchronous Support in Servlet 3.0″, http://blogs.sun.com/enterprisetechtips/entry/asynchronous_support_in_servlet_3

· Michele Simionato, “Threads, processes and concurrency in Python: some thoughts”, [weblog entry.] The Explorer. 26 Jul 2010. (http://www.artima.com/weblogs/viewpost.jsp?thread=299551). 26 Jul 2010.

· Orlic, Bojan; “SystemCSP : a graphical language for designing concurrent component-based embedded control systems”. (2007) thesis. http://doc.utwente.nl/58009/

· Jonas Bonér, “Introducing Akka – Simpler Scalability, Fault-Tolerance, Concurrency & Remoting through Actors”. 4 Jan 2010. (http://jonasboner.com/2010/01/04/introducing-akka.html). 14 Mar 2010.

· Stephan Schmidt, “Actor Myths”, [Weblog entry.] Code Monkeying. Jul 21, 2010. (http://codemonkeyism.com/actor-myths/)

· James Iry. “Erlang Style Actors Are All About Shared State”, [Weblog entry.] One Div Zero. 6 Apr, 2009. (http://james-iry.blogspot.com/2009/04/erlang-style-actors-are-all-about.html) . 23 Jul 2010.

· Paul Chiusano, “Actors are not a good concurrency model”, [Weblog entry.] Prettt-tty, pretty, pretty good!. 15 Jan 2010. (http://concurrency.tumblr.com/post/420147030/actors-are-not-a-good-concurrency-model). 2. Mar 2010.

· Welch, P.H.; “Process Oriented Design for Java: Concurrency for All”, http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.102.9787

· Dimitris Andreou, “Thoughts on Actors”, [Weblog entry.] Code-o-matic. 8 Jan 2010. (http://code-o-matic.blogspot.com/2010/01/thoughts-on-actors.html). 23 July 2010.

· McDonald, Carol; “Some Java Concurrency Tips”, http://weblogs.java.net/blog/caroljmcdonald/archive/2009/09/17/some-java-concurrency-tips

· Oprean, George and Pedersen, Jan B., “Asynchronous Active Objects in Java”, Communicating Process Architectures, 2008., http://wotug.org/paperdb/show_proc.php?f=4&num=26

· sutter, Herb; “Prefer Using Active Objects Instead of Naked Threads”, http://www.drdobbs.com/high-performance-computing/225700095;jsessionid=OCHVVY5DWODL3QE1GHRSKHWATMY32JVN

· Alex Tkachman, “Groovy concurrency in action: asynchronious resource pools with Groovy++”, http://groovy.dzone.com/articles/groovy-concurrency-action-0

· Alex Tkachman, “Fast immutable persistent functional queues for concurrency with Groovy”, JavaLobby, http://java.dzone.com/articles/fast-immutable-persistent

· Schumacher, Dale, “Composing Actors”, “blog It’s Actors All The Way Down”, http://www.dalnefre.com/wp/2010/05/composing-actors/

· “Objects as Actors?”, Debasish Ghosh, http://java.dzone.com/news/objects-actors

· “Gartner Says as the Number of Processors Swells Inside Servers, Organizations May Not Be Able to Use All Processors Thrust on Them”, http://www.gartner.com/it/page.jsp?id=867112

· “Tilera vs. Godzilla”, Louis Savain, http://rebelscience.blogspot.com/2007/08/tilera-vs-godzilla.html

· “Convergence in Language Design: A Case of Lightning Striking Four Times in the Same Place”, Peter Van Roy, http://www.info.ucl.ac.be/~pvr/flopsPVRarticle.pdf

· “The Problem with Threads”, Edward A. Lee, http://www.eecs.berkeley.edu/Pubs/TechRpts/2006/EECS-2006-1.pdf

· “A Component-Oriented Language for Pointer-Free Parallel Programming”, Luc BlÄaser, Computer Systems Institute, ETH ZÄurich, Switzerland. Accessed on 3/10/2009 at http://www.isp.uni-luebeck.de/kps07/files/papers/blaeser.pdf

· Mauricio Arango, “Coordination in parallel event-based systems”, http://blogs.sun.com/arango/entry/coordination_in_parallel_event_based

· Irfan Pyarali, Tim Harrison, and Douglas C. Schmidt Thomas D. Jordan; “Proactor: “An Object Behavioral Pattern for Demultiplexing and Dispatching Handlers for Asynchronous Events”, http://www.cs.wustl.edu/~schmidt/PDF/proactor.pdf

· “A Component-Oriented Model for the Design of Safe Multi-threaded Applications”, Reimer Behrends, R. E. K. Stirewalt and L. K. Dillon Dept. of Computer Science and Engineering Michigan State University, accessed on 3/10/2009 at http://www.cse.msu.edu/~stire/Papers/cbse05.pdf

· “2028: Concurrent processing–from revolution to legacy”, http://www.embedded.com/design/212000158

· “Join Patterns for Visual Basic”, accessed on 3/10/2009 at http://research.microsoft.com/en-us/um/people/crusso/papers/cb.pdf

· “ActorsModel”, at http://c2.com/cgi/wiki?ActorsModel

· “Sharing Is the Root of All Contention”,Herb Sutter, http://www.ddj.com/go-parallel/article/showArticle.jhtml?articleID=214100002

· Bryan Cantrill. “OpenSolaris Sewer Tour”. [weblog entry.] The Observation Deck. 14 Jun 05. (http://blogs.sun.com/bmc/entry/opensolaris_sewer_tour). 26 Jul 10.

· “Concurrent computing”, http://en.wikipedia.org/wiki/Concurrent_computing

Walsh, Matt; “SEDA: An Architecture for Highly Concurrent Server Applications”, Harvard University,
http://www.eecs.harvard.edu/~mdw/proj/seda/

· “Multicore programming: Easy or difficult?”, http://www.edn.com/article/CA6646279.html?nid=2551

· “The universe model: An approach for improving the modularity and reliability of concurrent programs, Reimer Behrends”, http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.15.8983

· Mitchell Pronschinske, “Concurrent Programming in Groovy”, JavaLobby, http://java.dzone.com/articles/dont-be-afraid-try-gpars

· “Actors in Groovy”, Alex Miller, http://tech.puredanger.com/2009/01/16/actors-in-groovy/

· “Scala Actors vs Plain Old Java”, Duke Banerjee, http://shorugoru.blogspot.com/2009/09/scala-actors-vs-plain-old-java.html

· Event-based actors in Groovy, Václav Pech, accessed on 3/4/09 at http://www.jroller.com/vaclav/entry/event_based_actors_in_groovy

· Pech, Václav; “Flowing with the data”, http://www.jroller.com/vaclav/entry/flowing_with_the_data

· “We haven’t forgotten about other models – honest!”, posted to Maestro blog, accessed on 3/02/2009 at http://blogs.msdn.com/maestroteam/archive/2009/02/27/we-haven-t-forgotten-about-other-models-honest.aspx

· ” Infrastructure for the Synchronization and Coordination of Concurrent Java Component Programs”, Sandeep Mitra, Sudhir Aggarwal, accessed on 2/28/09 at http://csdl.computer.org/comp/proceedings/hicss/2000/0493/08/04938052.pdf

· Parallel Computing Developer Center, http://msdn.microsoft.com/en-us/concurrency/default.aspx

· Search on CiteSeer for STM: http://citeseerx.ist.psu.edu/search;jsessionid=832BC25C661FF28D18EDAE10E725B301?q=software+transactional+memory&submit=Search&sort=rel

· “Synchronization and Time”, Duffy, Joe; http://www.bluebytesoftware.com/books/winconc/ConcurrentProgramming032143482X_ch02.pdf

· “Concurrency’s Shysters”, http://blogs.sun.com/bmc/entry/concurrency_s_shysters

· “More thoughts on transactional memory”, Duffy, Joe; http://www.bluebytesoftware.com/blog/PermaLink,guid,94778838-3e27-4788-a935-006ae9c8ef94.aspx

· “And now some Hardware Transactional Memory comments…”,Cliff Click Jr., http://blogs.azulsystems.com/cliff/2009/02/and-now-some-hardware-transactional-memory-comments.html

· “Communicating Java Threads” (1997),,Gerald Hilderink, Jan Broenink, Wiek Vervoort, Andre Bakkers, http://www.ce.utwente.nl/javapp/cjt/CJT-paper.PDF

· “Actors That Unify Threads and Events”,Philipp Haller and Martin Odersky, http://lamp.epfl.ch/~phaller/doc/haller07coord.pdf

· Discussion at Lambda the Ultimate: http://lambda-the-ultimate.org/node/2048

· “The Next Mainstream Programming Language”, http://www.cs.princeton.edu/~dpw/popl/06/Tim-POPL.ppt

· “Actor Foundry”,”Rajesh Karmani, et al.”,http://osl.cs.uiuc.edu/~rkumar8/ActorFoundry.ppt

· “Implementing the π-Calculus in Java”,Liwu Li, http://www.jot.fm/issues/issue_2005_03/article5.pdf

· “Tackling Concurrency Language or Library?”,http://www.scala-lang.org/sites/default/files/odersky/intel06.pdf

· “Programming in the Age of Concurrency: Software Transactional Memory”,http://channel9.msdn.com/shows/Going+Deep/Programming-in-the-Age-of-Concurrency-Software-Transactional-Memory/

· “Communicating Process Architectures 2008″, Editors: Frederick R. M. Barnes, Jan F. Broenink, Alistair A. McEwan, Adam Sampson, G. S. Stiles, Peter H. Welch; IOS Press, Amsterdam, 978-1-58603-90. http://wotug.org/paperdb/show_proc.php?f=4&num=26 Accessed 26 Jul 10.

· “CSP for Java programmers, Part 1“,Abhijit Belapurkar, http://www-128.ibm.com/developerworks/java/library/j-csp1.html

· “CSP for Java programmers, Part 2“,Abhijit Belapurkar, http://www.ibm.com/developerworks/java/library/j-csp2/

· “CSP for Java programmers, Part 3“,Abhijit Belapurkar, http://www.ibm.com/developerworks/java/library/j-csp3.html

· More Java Actor Frameworks Compared, http://sujitpal.blogspot.com/2009/01/more-java-actor-frameworks-compared.html, Sun Jan 04 2009 09:24:04 GMT-0500 (Eastern Standard Time)

· Concurrency, Actors and Kilim, http://sujitpal.blogspot.com/2008/12/concurrency-actors-and-kilim.html, Sun Jan 04 2009 09:24:54 GMT-0500 (Eastern Standard Time)

· Event-Based Programming without Inversion of Control,
Philipp Haller and Martin Odersky, Proc. JMLC 2006, and. Accessed 2007 at http://lampwww.epfl.ch/~odersky/papers/jmlc06.pdf

· Actors that Unify Threads and Events,
Philipp Haller and Martin Odersky, Proc. COORDINATION 2007. Accessed 2007 at http://lamp.epfl.ch/~phaller/doc/haller07coord.pdf

· “Integrating and Extending JCSP”, Peter WELCHa, Neil BROWNa, James MOORES b, Kevin CHALMERS c and Bernhard SPUTH. Communicating Process Architectures 2007. Accessed 2007 at xxxx.

· “Message Passing–Sync or Async?”, Bartosz milewski, http://bartoszmilewski.wordpress.com/2009/02/10/message-passing-sync-or-async/

· A message thread about Erlang related questions, http://www.erlang.org/pipermail/erlang-questions/2008-January/032224.html

· “Are Concurrent Programs That Are Easier to Write Also Easier to Check?”, Kedar S. Namjoshi, accessed 20081228 at http://www.cs.utah.edu/ec2/papers/ec2-pp7.pdf

· Goldman, Oliver. “Multithreading, Java, & OSGi.” http://www.ddj.com/java/191601642.

· Vogel, Lars. “Java Concurrency / Multithreading – Tutorial”, http://www.vogella.de/articles/JavaConcurrency/article.html

· “Thread-safety in OSGi”, Neil Bartlett, accessed at http://neilbartlett.name/blog/2007/03/05/thread-safety-in-osgi/

· Ernst, Dan.”Parallelism Exposure – It’s Not That Hard!“,

· “Kilim: Isolation-typed actors for Java”, Sriram Srinivasan, http://www.malhar.net/sriram/talks/kilim-google.pdf

· “Wot, no chickens?”, http://wotug.org/parallel/groups/wotug/java/discussion/3.html

· “Java for High Performance Computing”, http://mpj-express.org/

· “4.5 Active Objects”, http://gee.cs.oswego.edu/dl/cpj/s4.5.html

· “Rock (processor)”, http://en.wikipedia.org/wiki/Rock_processor

· “Early Experience with a Commercial Hardware Transactional Memory Implementation”,Dave Dice, Yossi Lev, Mark Moir, and Dan Nussbaum, http://blogs.sun.com/dave/resource/asplos09-Rock-Final2.pdf

· “Concurrency JSR-166 Interest Site”, http://gee.cs.oswego.edu/dl/concurrency-interest/index.html

· “Actors Guild”, http://actorsguildframework.org/

· Synchronous Active Objects Home Page, http://ltiwww.epfl.ch/sJava/index.html

· “What after Java? From objects to actors”,Carlos A. Varela and Gul A. Agha, http://www7.scu.edu.au/1890/com1890.htm

· “Programming Java threads in the real world, Part 9”, Allen Holub, JavaWorld.com, 06/01/99, http://www.javaworld.com/javaworld/jw-06-1999/jw-06-toolbox.html

· Actors Foundations for Open System: http://www.erights.org/history/actors.html

· “Power Combination: SCA,, OSGi and Spring”, OSOA Collaboration, http://www.osoa.org/download/attachments/250/Power_Combination_SCA_Spring_OSGi.pdf

· There Is a Silver Bullet, Brad J. Cox, http://www.ddj.com/184407534

· Concurrency and Coordination Runtime, http://en.wikipedia.org/wiki/Concurrency_and_Coordination_Runtime

· Yuri Gurevich, Wolfram Schulte, and Charles Wallace, “Investigating Java Concurrency using Abstract State Machines”. In Y. Gurevich, P. Kutter, M. Odersky, and L. Thiele, eds., Abstract State Machines: Theory and Applications, Springer LNCS 1912, 2000, 151-176.

· Understanding actor concurrency, Part 1: Actors in Erlang A new way to think about structuring concurrent applications By Alex Miller, JavaWorld.com, 02/24/09, http://www.javaworld.com//javaworld/jw-02-2009/jw-02-actor-concurrency1.html

· “Understanding actor concurrency, Part 2: Actors on the JVM”, http://www.javaworld.com/javaworld/jw-03-2009/jw-03-actor-concurrency2.html

· Byrne, Dennis; “Memory Barriers and JVM Concurrency”, InfoQ, http://www.infoq.com/articles/memory_barriers_jvm_concurrency

· Thread Safe Programming Language, Stefan Forster, http://threadsafeprogramming.blogspot.com/2009/03/threadsafeprogramminglanguage.html

· Maestro: A Special-Purpose Language for Parallel Programming, Jonathan Erickson, http://www.ddj.com/go-parallel/article/showArticle.jhtml?articleID=214502187

· Message Passing Interface (MPI), http://en.wikipedia.org/wiki/Message_Passing_Interface

· “Best programming approach/methodology to assure thread safety”, http://stackoverflow.com/questions/256517/best-programming-approach-methodology-to-assure-thread-safety/256684

· “RPC and its Offspring: Convenient, Yet Fundamentally Flawed”, Steve Vinoski”, http://qconlondon.com/london-2009/file?path=/qcon-london-2009/slides/SteveVinoski_RPCAndItsOffspringConvenientYetFundamentallyFlawed.pdf

· “Bigraphs: a model for mobile agents”, Robin Milner, Accessed on 3/3/2009 at http://www.cl.cam.ac.uk/~rm135/Bigraphs-Lectures.pdf

· “Fine-grain concurrency”, Tony Hoare, accessed on 3/3/2009 at http://se.inf.ethz.ch/laser/2007/slides/guildford.Fine-grain%20concurrency.pdf

· P. Brinch Hansen, A keynote address on concurrent programming. Keynote address for the IEEE Computer Software & Applications Conference, Chicago, IL, November 1978. Computer 12, 5 (May 1979), 50{56. Copyright °c 1979, Institute of Electrical and Electronics Engineers, Inc., accessed on 3/3/09 at http://brinch-hansen.net/papers/1978c.pdf

· “Concurrency: The Next Generation”, Damian Dimmich, Christian Jacobsen and Matthew Jadud, Computing Laboratory University of Kent Canterbury, CT2 7NZ, accessed on 3/3/09 at http://www.cs.kent.ac.uk/pubs/2006/2522/content.pdf

· “Concurrency and Erlang” LCA2007 Andre Pang, http://www.scribd.com/doc/415195/Concurrency-and-Erlang-LCA2007-Andrep

· “Concurrency in Erlang & Scala: The Actor Model”, Ruben Vermeersch, http://ruben.savanne.be/articles/concurrency-in-erlang-scala

· Erlang for Concurrent Programming, Jim Larson, http://queue.acm.org/detail.cfm?id=1454463

· How OSGi Changed My Life, Peter Kriens, http://queue.acm.org/detail.cfm?id=1348594

· “New parallel programming language design: a bridge between brain models and multi-core/many-core computers?”, http://arxiv.org/PS_cache/arxiv/pdf/0812/0812.2926v1.pdf

· Component-based software engineering, http://en.wikipedia.org/wiki/Software_componentry

· “Component-based approach for embedded systems”, Ivica Crnkovic Mälardalen University, Department of Computer Science and Engineering, http://research.microsoft.com/en-us/um/people/cszypers/events/wcop2004/18-crnkovic.pdf

· Super Actors for Real Time (2001), G. Fortino, L. Nigro, F. Pupo, D. Spezzano, Proc. of the 6 th IEEE Workshop on Object-oriented Real-time Dependable Systems (WORDS’01 http://si.deis.unical.it/~fortino/research/publications/conferences/pdf/words01.pdf

· “Fundamentals of Concurrent Programming for .NET” (2005), Charteris White Paper, Greg Beech, http://www.charteris.com/publications/white_papers/downloads/White Papers – Fundamentals of Concurrent Programming for dotNET (Greg Beech) March 2005.pdf

· “A type safe state abstraction for coordination in Java-like languages”,Ferruccio Damiani, Elena Giachino, Paola Giannini, and Sophia Drossopoulou,Acta Informatica, Volume 45, Numbers 7-8 / December, 2008, http://www.springerlink.com/content/2168q630k2355563/

Books

· The Art of Concurrency: A thread Monkey’s Guide to Writing Parallel Applications, Clay Breshears, O’Reilly Media, May 2009. 978-0-596-52153-0. http://oreilly.com/catalog/9780596521547

· Concurrency: State Models & Java Programs, Jeff Magee and Jeff Kramer

· Java Concurrency in Practice, Brian Goetz

· Concurrent Programming in Java, Doug Lea,

· Java Thread Programming, Paul Hyde,

· Java Threads, Oaks & Wong,

· Multithreaded Programming with Windows NT, Thuan Q. Pham and Pankaj K. Garg

· From “Industry Education Recommended Reading List”, http://www.intel.com/technology/rr/

o C# Threading Handbook, Tobin Titus, Sandra Gopikrishna, Tejaswi

o Redkar, Srinivasa Sivakumar, Wrox Press 1861008295

o Computer Architecture: A Quantitative Approach 4th Edition John L. Hennessy and David Patterson Morgan Kaufmann 0123704901

o Multi-Core Programming Shameem Akhter, Jason Roberts Intel Press 0976483246

o Multithreading Applications in Win32: The Complete Guide to Threads Jim Beveridge, Robert Wiener Addison-Wesley Professional 0201442345

o Parallel Programming in C with MPI and OpenMP Michael J. Quinn McGraw-Hill Professional 0072822562

o Parallel Programming in OpenMP Rohit Chandra, Ramesh Menon, Leo Dagum, Dave Kohr, Dror Maydan, and Jeff McDonald Morgan Kaufmann 1558606718

o Using OpenMP: Portable Shared Memory Parallel Programming Barbara Chapman, Gabriele Jost, Ruud van der Pas, David J. Kuck MIT Press 0262533022

o Parallel Programming with MPI Peter Pacheco Morgan Kaufmann 1558603395

o Patterns for Parallel Programming Timothy G. Mattson, Beverly A. Sanders, Berna L. Massingill Addison-Wesley Professional 0321228111

o The Art of Concurrency Clay Breshears O’Reilly 9780596521530

o Programming with Hyper-Threading Technology Andrew Binstock, Richard Gerber Intel Press 0971786143

o Programming with POSIX® Threads David R. Butenhof Addison-Wesley Professional 0201633922

o The Software Optimization Cookbook, Second Edition Richard Gerber, Aart J.C. Bik, Kevin Smith, Xinmin Tian Intel Press 0976483211

o Optimizing Applications for Multi-Core Processors Stewart Taylor Intel Press 1934053015

o Intel Threading Building Blocks: Outfitting C++ for Multi-Core Processor Parallelism James Reinders O’Reilly 0596514808

o Threads Primer: A Guide to Multithreaded Programming Bil Lewis, Daniel J. Berg Prentice Hall 0134436989



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